DE68905163T2 - STERILIZATION METHOD. - Google Patents

Description

Technical part

This invention relates generally to sterilization processes and preferably to a sterilization process for packages using hydrogen peroxide as a sterilant.

State of the art

The previous method of blowing hot air into a box in which hydrogen peroxide had been sprayed causes the liquid hydrogen peroxide to immediately evaporate and be expelled from the box. The time required is uncontrollable and too short for effective sterilization.

Methods other than creating a hydrogen peroxide and water vapor atmosphere inside the carton have been tried. Such other method involves creating a hydrogen peroxide vapor in a circulating loop and applying this vapor to an open carton, which must cause condensation to disperse the hydrogen peroxide inside the carton. This was not effective and gave a minimal kill rate.

Various methods of dipping and/or spraying the sterilant hydrogen peroxide in conjunction with heating are described in US-A-4,169,123; US-A-4,225,556; US-A-3,566,575; US-A-4,566,251; and US-A-4,631,173.

US-A-3 899 862 discloses a method and apparatus for continuously cold sterilizing, aseptically filling and dosing containers, in which each subsequent container is dosed by a dosing device with an amount of sterilizing agent, which is retained within the container for a time sufficient for sterilization to take place, is conveyed through a tunnel in which a gaseous environment is maintained under slight overpressure, is filled and has a sterile lid which is fitted under sterile conditions within the tunnel.

The dosing device doses either a jet of undiluted sterilizing gas, e.g. hydrogen chloride, or a microdrop of a gas-generating liquid. After dosing, the containers are kept closed for a certain period by a temporary closure means. This can be done in various ways. A film can be spread over the container openings. To enable the renewal of this film, the possible wear of which is caused by the containers passing beneath it, it is fed from a feed roller to a winding roller. The film can be kept pressed onto the container openings by means of sterile air from a blowing device or by means of an elastic block. Alternatively, an endless belt made of, for example, impermeable PVC foam, which closes the container openings, can advance with the containers. The sterilizing agent is washed out of the sterilized containers by jets of dry sterile air from a plurality of nozzles.

Disclosure of the invention

An object of the present invention is to provide an improved high speed sterilization process that is efficient and effective for open ended thermoplastic coated paperboard packages.

Another object of the invention is to provide an improved method of sterilization which can be used in conjunction with a conventional conveyor type form-fill-seal machine having an intermediate operation of forming and sealing one end and filling and forming and sealing the other end on the machine, such as the intermediate sterilization section of US-A-4 556 251.

Another object of the invention is to provide a high-speed sterilization process that achieves a reproducible spore reduction index of at least 8D with hydrogen peroxide residues below 0.1 ppm in conventional cardboard packaging.

According to the present invention there is provided a sterilization method comprising introducing a sterilizing agent at room temperature into open ends of containers having opposite ends closed, conveying the containers along a stationary closure member with the open ends substantially closed thereby while sterilization takes place, flushing the containers with sterile air and conveying the sterilized and flushed containers through filling stations and open end closing stations, characterized in that introducing the sterilizing agent comprises spraying therein a solution of hydrogen peroxide, made of cardboard, that while the closure member substantially closes the containers, the outer surfaces of the containers are exposed to hot sterile air at a first temperature, and then the outer surfaces of the containers are exposed to sterile air at a second temperature which is higher than room temperature but lower than the first temperature, that rinsing comprises drying the containers with sterile air at a third temperature between the first and second temperatures and as it is directed into the open ends thereof, provides a desired final maximum in parts per million of hydrogen peroxide, and that the sterilized and dried containers are transferred to a conveyor system which is capable of transporting the containers through the filling stations and the open end closing stations.

Preferably, the sterilization process comprises the steps

(a) spraying air containing up to 35% hydrogen peroxide solution, giving a concentration of 300 to 400 parts per million, at room temperature or approximately 21ºC (70ºF), into open-ended paperboard cartons after the cartons have exited the typical tower on which one end closure has been formed and sealed;

(b) moving each carton through an external heating section, directly below a stationary sealing element, while hot air at a temperature in the range of 171-204ºC (340-400ºF) is blown upwards and laterally past the packages, thereby raising the internal temperature of the hydrogen peroxide film to about 71ºC (160ºF);

(c) conveying the cartons beneath the stationary sealing element which extends through a sterilization section with which it is in very close contact and exposing the external surfaces of the cartons to air at a temperature in the range of 93-110 ºC (200-230 ºF), thereby raising the internal temperature of the hydrogen peroxide film to approximately 88 ºC (190 ºF);

(d) conveying the cartons away from the closure member into a drying section and drying the cartons with sterile air directed into the open ends of the cartons at a temperature in the range of 93-116ºC (200-240ºF), thereby raising the internal temperature of the hydrogen peroxide film to about 99ºC (210ºF) and achieving a maximum concentration of the hydrogen peroxide of 0.05 parts per million; and

the transfer of the sterilized and dried cartons from the drying section to a conveyor system suitable for transporting the cartons through the filling and closing stations.

Short description of the drawings

In order that the invention may be clearly understood and easily carried out, reference will now be made, by way of example, to the attached drawings, in which:

Figure 1 is a block diagram representation of the steps comprising a sterilization process including an optional intermediate step;

Figure 2 is a schematic representation of the apparatus used to carry out the method with the embodiment in Figure 1;

Figure 3 is an enlarged cross-sectional view taken along the plane of line 3-3 in Figure 2 looking in the direction of the arrow; and

Figure 4 is an enlarged view of part of the device in Figure 2.

Best mode for carrying out the invention

Referring to Figure 1, a block diagram is shown describing the following sequential steps:

A. Spraying an approximately 35% solution of hydrogen peroxide producing a concentration of 300-400 parts per million at room temperature, i.e. 21ºC (70ºF), into the open tops of the paperboard cartons after they have been stripped by the respective mandrels of a form, fill and seal turret on which one of the end closures of the cartons has been formed and sealed;

B. passing each carton through an external heating section, beneath a stationary sealing member in close contact therewith, while hot air at a temperature in the range of 171-204ºC (340-400ºF) is blown upwardly past the packages, thereby raising the internal temperature of the hydrogen peroxide film to about 71ºC (160ºF);

C. passing the cartons through a sterilization section beneath a stationary sealing member in very close contact therewith and exposing the external surfaces of the cartons to sterile air at a temperature in the range of 99-110ºC (210-230ºF) thereby raising the internal temperature of the hydrogen peroxide film to about 88ºC (190ºF);

D. Conveying the cartons away from the sealing element and drying the cartons with sterile air directed into the open ends of the cartons at a Temperature in the range of 93-116 ºC (200-240 ºF), which increases the internal temperature of the hydrogen peroxide film to about 99 ºC (210 ºF) and reduces hydrogen peroxide to a range of 0.01 - 0.05 parts per million; and

E. Transferring the sterilized and dried cartons from the drying section to a conveyor system suitable for transporting the cartons through the filling and sealing stations.

As Figure 1 further illustrates, step D above can be converted to two stations of inward air at 149-160ºC (300-320ºF), raising the internal temperature of the hydrogen peroxide film to about 93ºC (200ºF); followed by two rather than six stations of inward air at 105-116ºC (220-240ºF), reducing the hydrogen peroxide to a minimum concentration of 0.05 parts per million.

Referring now to the apparatus 10 used for the above-described process as shown in Figure 2, there is shown a loading section 12, a spray section 14, an external heating section 16, a sterilization section 18, a drying section 20 and a transfer section 22 with conveyor means shown at 23, with a conveyor cycle of 3.2 seconds. A pair of spray nozzles 24 and 26 are spaced from the center of the packages on mutually opposite sides of the center so that as each package progresses they spray the hydrogen peroxide in step A twice into each package in the spray section 14 for optimum internal surface coverage.

A hot air plenum 28 and discharge units 30 are operatively connected below the closed and above the open ends of the packages, respectively, with hot air from the hot air plenum being directed past the packages to the discharge units for the external heating process in section 16 as described above in step B. This air is alternately directed at angles of 5º below and 5º above the horizontal at alternating positions as illustrated by the exits 32 and 34 of the hot air plenum 28 in Figure 2 and shown in Figure 3.

A stationary sealing member 36 is mounted alongside each external heating section 16 and the sterilization section 18, past which the cartons move in very close contact therewith, with sterile air as described above in step C, provided from a hot air plenum 38 into the discharge units 40 through the hot air plenum outlets 32 and 34.

As shown in Figure 3, in addition to the hot air flowing lengthwise past the packages from their closed to their open ends, hot air can be directed laterally from the outlet 42 past the sides of the packages, particularly during the conveyor cycle idle periods for each of the seven stations of section 16 and the eight stations of section 18.

A hot air plenum 44 in the drying section 20 serves to admit sterile air into the open tops of the packages through a plurality of outlets 46a, 46b, 46c, 46d, 46e and 46f. In particular, the outlets are spaced variously from the centers of the respective packages when they pause beneath the outlets, as shown in Figure 4, thereby providing an effective movement pattern of sterile air within the packages.

Industrial applicability

It should be apparent that the invention provides an efficient and effective sterilization arrangement suitable for attachment to a form, fill and seal machine, intermediate turrets for forming and sealing the ends and filling and stations for sealing the other ends thereof.

Preferably, in this arrangement, the packages are sprayed with up to a 35% solution of hydrogen peroxide and conveyed in cycles to heating stations where the carton is sealed to retain a vapor atmosphere generated by hydrogen peroxide and water. Hot air is directed to the outer surfaces of the packages in a precise manner to also increase the internal surface temperatures of the packages. The liquid hydrogen peroxide and water mixture is vaporized as the internal surface temperature increases. The water vaporizes more easily at lower temperatures and as the internal surface temperature of the package increases upon heating, the liquid mixture of hydrogen peroxide remaining on the package surface becomes increasingly more concentrated. The increase in the concentration of hydrogen peroxide contributes to a higher microbiological kill rate.

As the peroxide vapor inside the carton increases, so does its partial pressure. This leaves the liquid peroxide on the surfaces of the package to evaporate at even higher temperatures. The peroxide liquid at higher temperatures, in close contact with the inner surfaces of the package, results in an even higher kill rate.

The steam circulating inside the packaging condenses on the colder surfaces of the packaging. This causes these colder surfaces to heat up and improves their respective kill rate.

The circulating peroxide vapor inside the cardboard volume has an additive sterilizing effect on these hot surfaces on which the peroxide liquid has completely evaporated.

The sterilizing factors (1) the concentration of the liquid peroxide sterilant, (2) the temperature at which the sterilization takes place, (3) the close contact of the sterilant with the surface to be sterilized, and (4) the time elapsed in the sterilization process are all controlled by this external heating process.

While only one embodiment of the invention has been shown and described, other modifications thereof are possible within the scope of the following claims.

Claims (23)

1. A sterilization method comprising introducing a sterilizing agent at room temperature into open ends of containers having opposite ends closed, conveying the containers along a stationary closure member whereby the open ends are substantially closed while sterilization takes place, flushing the containers with sterile air and conveying the sterilized and flushed containers through filling stations and open end closing stations, characterized in that introducing the sterilizing agent comprises spraying therein a solution of hydrogen peroxide, that the containers are made of cardboard, that while the closure member substantially closes the containers, the outer surfaces of the containers are exposed to hot sterile air at a first temperature, and then the outer surfaces of the containers are exposed to sterile air at a second temperature which is higher than room temperature but lower than the first temperature, that flushing comprises drying the containers with sterile air at a third temperature between the first and second temperatures and as it is directed into the open ends thereof, a desired final maximum in parts per million of hydrogen peroxide and that the sterilized and dried containers are transferred to a conveyor system capable of transporting the containers through the filling stations and the open end closing stations. 2. A method according to claim 1, wherein the spraying is carried out on a form, fill and seal machine immediately after the open-sided containers are stripped from their respective mandrels on which their opposite ends were formed and sealed. 3. A method according to claim 1 or 2, wherein the solution of hydrogen peroxide is about a 35% solution, giving a concentration in the range of 300-400 parts per million. 4. A process according to any one of the preceding claims, wherein the first temperature is in the range of 171-204ºC (340-400ºF). 5. The method of claim 4, wherein the containers achieve an internal hydrogen peroxide film temperature of about 71°C (160°F). 6. A process according to any one of the preceding claims, wherein the second temperature is in the range of 93-110ºC (200-230ºF). 7. The method of claim 6, wherein the containers achieve an internal film temperature of hydrogen peroxide of about 88ºC (190ºF). 8. A process according to any one of the preceding claims, wherein the third temperature is in the range of 93-116ºC (200-240ºF). 9. The method of claim 8, wherein the containers achieve an internal film temperature of hydrogen peroxide of about 99°C (210°F). 10. A process according to any one of the preceding claims, wherein the desired final maximum is 0.05 parts per million. 11. A method according to any one of the preceding claims, wherein the spraying takes place via two switching stations. 12. A method according to any one of the preceding claims, wherein the exposure to hot sterile air at the first temperature occurs over seven switching stations. 13. A method according to any one of the preceding claims, wherein the exposure to sterile air at the second temperature occurs over eight switching stations. 14. A method according to any one of the preceding claims, wherein the drying with sterile air at a third temperature takes place over six switching stations. 15. A method according to any one of claims 11 to 14, wherein the time for each conveying cycle is about 3.2 seconds. 16. A method according to any one of claims 1 to 13, further comprising drying the containers with sterile air at a temperature in the range of 149-160 ºC (300-320 ºF) introduced into the open tops of the containers, between exposure to sterile air at a second temperature and drying with sterile air at a third temperature. 17. The method of claim 16, wherein drying with sterile air occurs at a temperature in the range of 149-160ºC (300-329ºF) over two cycle stations. 18. A method according to claim 16 or 17, wherein drying with sterile air at a third temperature takes place over two switching cycle stations. 19. The method of claim 16, 17 or 18, wherein the containers achieve an internal film temperature of hydrogen peroxide of about 93°C (200°F). 20. A method according to any one of claims, wherein the sterile air at the first temperature and the sterile air at the second temperature are provided by a continuous flow of hot air from the adjacent opposite ends of the containers beyond the outer surfaces thereof. 21. A method according to claim 20, wherein the hot air is directed in one direction or the other at alternating switching stations during the exposure to the sterile air at the second temperature and the drying with sterile air at the third temperature, each deviating by 5º from the vertical. 22. The method of claim 20, further comprising blowing hot air laterally past the outer surfaces of the containers between the conveying strokes. 23. A method according to any one of claims 1 to 20, wherein during drying with sterile air at the third temperature, the sterile air is directed into the open ends of the containers in such a way that there is an alternation between advancing and retarding the container center so that the container interior is uniformly covered.